Fixed slave to properly acknowledge status updates sent by unknown
executors.

Review: https://reviews.apache.org/r/13554
Fixed slave to properly handle queued tasks during recovery
and KillTask().

Review: https://reviews.apache.org/r/13609
Added a 'ignorePartial' option to protubuf::read().

Review: https://reviews.apache.org/r/13623
Fixed slave state recovery to allow for partial status updates writes.

Review: https://reviews.apache.org/r/13624
Reverted the default recovery mode to strict.

Review: https://reviews.apache.org/r/13622
Added upgrade instructions for 0.14.0.

Conflicts:
	docs/Upgrades.md

Review: https://reviews.apache.org/r/13621
Fixed logging that ignored h_errno.
Updated CHANGELOG for 0.14.0.

Review: https://reviews.apache.org/r/13625
Fixed a bug in the implemntation of the Value::Set <= operator.

Review: https://reviews.apache.org/r/13629/